The people from 10,000 to 20,000 years ago are just as smart and intelligent as modern humans, and likely much smarter than many modern peoples today. They are no different than us. They just don't have the advantage of the accumulated knowledge we have now. It is very easy to underestimate the knowledge of those humans as just dumb cave men. Pretty much every decisions they made was life or death with no Mulligans or do overs.
This is just 358 years ago, but every era likely had a Newton, or Aristotle. We just don't know about them as they are lost to history.